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Lazy eye

The brain and eyes have to work together to produce clear vision. If the brain favors one eye — usually due to poor vision in the other eye — the weaker eye tends to wander inward or outward.

What is it?

The brain and eyes have to work together to produce clear vision. If the brain favours one eye — usually due to poor vision in the other eye — the weaker eye tends to wander inward or outward. Eventually, the brain may ignore the signals received from the weaker eye. This condition is sometimes referred to as lazy eye (amblyopia).

Lazy eye is the leading cause of decreased vision among children. And lazy eye is fairly common, affecting about two to three of every 100 children, according to the National Eye Institute.

Conservative treatments such as corrective eyewear or eye patches can usually correct lazy eye. Sometimes, lazy eye requires surgical treatment. Left untreated, lazy eye may lead to permanent vision impairment.

Symptoms

Signs and symptoms of lazy eye include:

An eye that wanders inward or outward

Eyes that may not appear to work together

Poor depth perception

Although lazy eye usually affects just one eye, it's possible for both eyes to be affected.

Causes

Anything that blurs a child's vision or causes the eyes to cross or turn out may cause lazy eye.

The most common culprit is strabismus — an imbalance in the muscles responsible for positioning of the eyes, which can cause the eyes to cross in or turn out. The muscle imbalance prevents the eyes from tracking with each other.

Sometimes lazy eye is the result of an anatomic or structural abnormality, such as an abnormal central retina or a cloudy area in the lens of the eye (cataract). In other cases, an abnormal eye shape or a size difference between the eyes contributes to lazy eye.

Risk factors

Lazy eye tends to run in families. Lazy eye may be more likely among children who were born prematurely or those who have developmental delays as they get older.

Occasionally, a wandering eye is the first sign of an eye tumour.

Complications

Left untreated, lazy eye can cause permanent vision loss. In fact, lazy eye is the most common cause of single-eye vision impairment in young and middle-aged adults, according to the National Eye Institute.

Diagnosis

Lazy eye is diagnosed with a thorough eye exam. The doctor will look for a wandering eye, as well as a difference in vision between the eyes or poor vision in both eyes. Special diagnostic tests aren't usually needed.